Their are two things which you should look for.
First:
Open your IIS(7.5).
Select Root/Server level.
Select "IsAPI and CGI Restrictions" from Right Panel.
Allow permissions.
Second:
When you run your Asp.Net application from IIS, your HttpModule needs to be registered in
"system.webServer" section of
web.config as below.
<system.webserver>
<modules runallmanagedmodulesforallrequests="true">
<add name="NameOfHttpModule" type="TypeOfHttpModule" />
</modules>
</system.webserver>
This should resolve your problem.